A U.S. senator from Oregon has proposed legislation that would give states a free hand to allow legal marijuana markets without the threat of federal criminal intervention.

The proposal by Sen. Ron Wyden aims to ease the conflict between the U.S. government and the growing number of states where cannabis is legal in some form.

The Democrat says the federal prohibition of marijuana "is wrong, plain and simple" and "too many economic opportunities have been missed."

The proposal would remove federal criminal penalties for individuals and businesses acting in compliance with state marijuana laws. It would also reduce barriers for legal marijuana businesses to get access to banking.

A separate bill would impose a tax on marijuana products similar to federal excise taxes on alcohol.